This invention relates generally to a method for manufacturing a camshaft and more particularly to a method for manufacturing a camshaft having added wear resistance at a lobe area of the camshaft.
Manufacturing processes for components of an internal combustion engine have evolved through the years so that such engine components can meet ever increasing performance requirements, e.g., increased stress tolerances and the like. These manufacturing processes have made the internal combustion engine more reliable and efficient; however, current manufacturing processes require additional steps or processes to add wear resistance properties to specific components of the internal combustion engine such as, for example, the camshaft of the internal combustion engine and more specifically the lobe regions of the camshaft. By providing added wear resistant properties to the camshaft, the internal combustion engine would be even more efficient than which is currently possible.
Being more specific, the lobe regions of the camshaft are subject to metal fatigue due to extensive contact between the lobes of the camshaft and respective rocker arms of the intake and exhaust valves. This contact wears down the lobe regions of the camshaft thus resulting in poor engine performance. However, current manufacturing processes do not address these problems and, in particular, do not provide a means for providing wear resistance properties at a particular region, e.g., lobes, of the camshaft.
By way of example, current casting processes do not provide adequate wear resistance properties at the lobe region of the camshaft. For example, in green sand casting processes a pattern which conforms to the external shape of the camshaft is formed. The pattern is then used to form a green sand mold which is made in an open frame or flask such that both the flask and the pattern are capable of being parted to facilitate removal of the pattern from the sand. A molten metal such as iron is then poured into the formed sand mold and, after solidifing, the cast iron is removed from the mold. Depending on the particular application of the camshaft, hardening materials may be added to the iron. The hardening materials, however, migrate to the bottom of the mold resulting in an uneven distribution of the hardening materials within the iron. By adding the hardening material, the integrity of the camshaft may be negatively impacted due to the uneven distribution of materials within the camshaft.
In another method of manufacturing camshafts, a camshaft is forged using known forging techniques. In particular, in known forging techniques a die is first formed, and a forging material such as alloys, aluminum or steel is heated to a desired temperature. The heated material is placed under pressure within the die until the forging material conforms to the shape of the die. The forging process is unable to provide added wear resistance properties to specific regions of the forged component such as the lobe regions of the camshaft. This is mainly due to the fact that the forging process cannot precisely place wear resistant material in specific locations which would correspond to the lobes of the camshaft.
U.S. Pat. No. 5,004,370 to Swars issued on Apr. 2, 1991 discloses a hollow shaft having drive elements (e.g., cams) with axially varied properties. The drive elements are secured on the hollow shaft by expansion of the hollow shaft, and includes a separate outside layer produced by an induction-hardened process. This outside layer, however, is not distributed throughout the drive elements, nor is it distributed within the hollow shaft. Accordingly, the apparatus of Swars has a tendency to wear during the use of the internal combustion engine, and does not appear to adequately withstand high torsional stresses.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention a method for manufacturing a camshaft is provided. The method includes forming an integrated mixture of a base material having a first density and a wear resistant material having a second density. The method has the steps of metering the integrated mixture into a die having an interior shape corresponding to a shape of the camshaft, and rotating the die. The rotation of the die forces the wear resistant material to migrate toward the outside of the lobe. After the rotating step, the camshaft is removed from the rotating die when the integrated mixture is solidified.
In another aspect of the present invention, the method of manufacturing a camshaft having a wear resistant lobe uses a rotating assembly having a rotating die. The rotating die has an interior shape corresponding to the camshaft. The method of making the crankshaft mixes a base material and a wear resistant material to form an integrated mixture. The wear resistant material is harder than the base material. The integrated mixture is metered into the rotating die, and the rotating die is then rotated so that the wear resistant material is forced toward an outer surface of the lobe. After the integrated mixture is solidified, the camshaft is removed from the rotating die.